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Residents at one home, at which two people are believed to reside (Table 2), have been exposed
in the past to VOCs in their private well water. The source of the contamination has not yet been
conclusively determined, but we feel that we can provide information on those exposures
regardless of what the source or sources are. The following discussion provides toxicological
information on the contaminants that exceeded comparison values, which are developed by
ATSDR. Therefore, the following discussion is limited to health concerns related to ingestion of
contaminated groundwater. Only the exposure pathway for ingestion of groundwater is
addressed (Table 3).

Only one well sample has been taken at this residence, and not enough information is available to
address the length of exposure that residents at the home would have experienced. To address
the potential for adverse health effects to occur, we can only use the data obtained from the single
well sampling event. No additional data are available for the levels of exposure to well
contaminants, if any, in the past.

The chemical present at levels exceeding comparison values in groundwater at the residence is
trichloroethylene. The comparison values are used only to screen for contaminants that should be
further evaluated and do not represent thresholds of toxicity. Levels of exposure above these
values do not indicate that adverse health effects can be expected. Because past exposures may
have occurred, this contaminant requires discussion. We reviewed the scientific literature,
comparison values, and possible health effects associated with the contaminant selected for
evaluation. The results of our review are presented in this section.

No MCLs were exceeded for any compounds found in the drinking water sample, but the
comparison value for trichloroethylene was slightly exceeded. This comparison value is one that
is determined for suspected carcinogenic substances and is highly conservative. Comparison
values for suspected carcinogens are based usually on an assumption that the reference population
would receive a lifetime of daily exposure, which is not the case in this exposure situation. Also,
these values are adjusted to account for variation in sensitivity among the members of the human
population, extrapolation of animal data to the case of humans, and extrapolation from data
obtained in a study that is less than lifetime exposure.

Although the comparison value for trichloroethylene was exceeded in the single well sample at
this residence, it is unlikely that adverse health effects would occur from this level of exposure.
An estimated daily dose was calculated for exposure to trichloroethylene at the level recorded in
the well sample, and it did not exceed the minimal risk level (MRL) (Appendix A) developed by
ATSDR. There is not sufficient information available to determine if excess risk for developing
cancer due to exposure to trichloroethylene should be expected. Scientist are uncertain whether
people who breathe air or drink water containing trichloroethylene are at higher risk of getting cancer or of developing reproductive effects (5).